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Old Dec 22, 2003, 01:15 AM
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South Africa
Joined Aug 2003
587 Posts
rysium

Looking at your efficiency values, I did a quick calc. and come out at a very different value. The efficiency formula I use is

Prop dia to power of 4 --- multiplied by pitch --- multiplied by rpm to power of 3 --- multiplied by prop factor K. -- typical 1.11 (found via a link somewhere here)

All measurements in feet and RPM in thousands.

Thus

Diameter = 9 inch = 9/12 y/x of 4 = 0,316
Pitch = 4.7 = 4.7/12 = 0.3916
RPM = 4620 = 4.620 y/x of 3 = 98.61

Therefore efficiency = 0,316 x 0,3916 x 98.61 = 12.20 Watts to prop

K factor included (depending on prop) = 13.5 Watts to prop.

Efficiency therefore = 35%

Now have I got something wrong? If I have got it wrong, then my motor is looking awfully good for a CD-rom. So somebody please give me the real formula.
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